Kantan is a Chinese-style compound (on-reading) meaning 'simple'. It is normally written in characters as 簡単, a form that is frequently encountered, as in the following notice:
Given that kantan is a Chinese-style compound, it is somewhat surprising to find that it is also often written in hiragana as かんたん.
The motive for writing the word in hiragana may be to emphasise how clean and simple it is to apply for the services advertised (automatic debiting of bank accounts). There is also the fact that kantan is a very familiar word in everyday life, which makes it easier to dispense with Chinese characters.
In other signs, kantan is found written in katakana:
A Google search in August 2003 reveals that the use of both hiragana and katakana to write the word kantan is relatively common, at least on the Internet: